1. Field of the Invention
Embodiments of the invention generally relate to a material withdrawal apparatus and method of such. Particularly, the invention relates to material withdrawal apparatus and methods of metering and withdrawing one or more materials from one or more units, such as fluid catalytic cracking (FCC) units, and other units such as manufacture of acrylonitrile, as manufacture of pyridine and its derivatives, and other industrial processes, etc.
2. Description of the Related Art
FIG. 1 is a simplified schematic of a conventional fluid catalytic cracking system 130. The fluid catalytic cracking system 130 generally includes a fluid catalytic cracking (FCC) unit 110 coupled to a catalyst injection system 100, a petroleum feed stock source 104, an exhaust system 114 and a distillation system 116.
The FCC unit 110 includes a regenerator 150 and a reactor 152. The reactor 152 primarily houses the catalytic cracking reaction of the petroleum feed stock and delivers the cracked product in vapor form to the distillation system 116. Spent catalyst from the cracking reaction is transferred from the reactor 152 to the regenerator 150 to regenerate the catalyst by removing coke and other materials. The regenerated catalyst is reintroduced into the reactor 152 to continue the petroleum cracking process to burn off coke from the catalyst. The regenerated catalyst is then reintroduced into the reactor 152 to continue the petroleum cracking process.
The fluid catalytic cracking system 130 generally includes a FCC unit 110 coupled to a catalyst injection system 100 that maintains a continuous or semi-continuous addition of fresh catalyst to the inventory circulating between a regenerator 150 and a reactor 152.
During the catalytic process, a dynamic balance of the total catalyst within the FCC unit 110 is maintained. For example, catalyst is periodically added utilizing the catalyst injection system and some catalyst is lost in various ways such as through the distillation system, through the effluent exiting the regenerator 150, and deactivation of the catalyst, etc. If the amount of catalyst within the FCC unit 110 decreases over time, the performance and desired output of the FCC unit 110 will diminish, and the FCC unit 110 will become inoperable. Conversely, if the catalyst inventory in the FCC unit 110 increases over time, the catalyst bed level within the regenerator reaches an upper operating limit and the excess or deactivated catalyst may be withdrawn to prevent unacceptably high catalyst emissions into the flue gas stream, or other process upsets.
Thus, a need exists for a material withdrawal apparatus and method suitable for withdrawing materials from one or more units, like FCC units. Furthermore, a need also exists for a material withdrawal apparatus and method suitable for withdrawing materials from one or more units under a low oxygen environment condition, such as partial burn or partial combustion and poor air circulation.